DIY CO2 Probe Information, For What It Is Worth

Hi,

I have had a couple of email requests for information on my do-it-yourself CO[SUB]2[/SUB] probe experience.

Notice I went out and bought a CO[SUB]2[/SUB] meter, so I cannot claim great diy success.

First off, my interest and most of my original information came from Vaughn of Hoppy fame. I also got a lot of information from various internet posts and I cannot find the other primary resource that as I recall was a Russian language source.

My membrane trials were based on or natural offshoots of a couple of lists posted by Tom Barr as “Plantbrain” elsewhere.

I had noticed my “test tube” drop checkers had quicker response time, so Hoppy’s observation made sense.

So, based on Hoppy’s observation that high surface area to reference solution volume I first tried setting up drop checkers based on surface area to reference solution volume.

• Low and behold, Hoppy was correct.:surprise:

The simplest form being like this DIY Co2 Meter where it is easy to vary surface area to reference solution volume and since the reference solution does not have to be read, the volume of reference solution only need to be sufficient to cover the probe element.

For pH probes, I had a Hanna pH meter, a diy pH probe and a Milwaukee meter.

It appears that most LDPE (low-density polyethylene), LLDPE (Linear low-density polyethylene ) is even better work so all kinds of sandwich wraps and bags work films work to one degree or another, the "Saran Wrap" style being the worst, almost unusable, to thinner, true LLDPE wraps working reasonably well, obviously the thinner the better.

I cannot locate the DO membrane from Hach I tried; I think they were something like Standard DO membrane kit for DO probe 05521-00, I found these too fragile for a complete lummox as I to handle.

Parafilm is another I have not tried, but have heard good reports, in fact I lost the reference but it seems quite successful.

It appears gsjimia references an interesting product in the thread “CO2 tester using PH probe,” post #2. That is likely better than anything I tried.

Of the things I tried, the best all round, is a product called Tyvek, readily available from home improvement stores and in various types of clothing and in mailers, as in the lined priority mail, mailers. The stuff is tough, keeps water out and gas, CO[SUB]2[/SUB] anyway move through quickly. :beguiled:

As always these things depend on high surface area to reference solution volume and the accuracy of the 4-dKH, or whatever reference solution chosen.

In making a reference solution with baking soda, I think it is worth drying it out even in the dry area I live I can see a difference. There is some bogus information out on the internet regarding drying baking soda.

Never let the temperature exceed 70⁰C (158⁰F), somewhere around 70-80⁰C baking soda loses CO[SUB]2[/SUB], of course this is why we like it for baking, but it is bad form for our purposes. So, we must gently force the excess moisture out of the baking soda without turning it into Sodium carbonate.

• Place twice as much baking soda as you think you need, on a nonreactive surface, I like parchment paper on a cookie sheet.
• Most ovens in the US, I am familiar with start at 150⁰F (65.6⁰C) that is the temperature I use.
• Leave for 2-hours
• Weigh the amount you require, return the excess to its container.

Making the largest the initial quantity of solution the greater the likely accuracy of the reference solution. While I know 50-liter, solutions are a bit much…

• A little less than 5-grams (4.989-g) of baking soda, then add enough distilled water to make 5-liters (~4.995-l).

OR

• A little less than 2.5-grams (2.494-g) of baking soda, then add enough distilled water to make 2.5-liters (~2.498-l).

OR

• A little less than 1-gram (0.998-g) of baking soda, then add enough distilled water to make 1-liter (~0.999-l).

All three solutions result in 40-dKH.

For the 4-dKH reference solution

• mix 1 part 40-dKH solution with 9 parts distilled water
  • Mix 10-ml 40-dKH solution with 90-ml of distilled water, for example.

Biollante

 

That My Friend is the $64,000 Question

Hi,

Given the high price of CO[SUB]2[/SUB] meters and probes, I suspect for most reasonable purposes the do it yourself probes, seem a reasonable alternative.

I think the demand for 4-second response time is a tad unrealistic, but I suspect that with the type of material you have ordered you should easily get under 10-seconds, with little bounce. Part of the response time involves the pH meter and probe.

I think you can do better than a bag around the probe. It rather depends on the shape of your probe, but from what I could tell it seemed an advantage to have some structure around the probe. I think one of the better designs I had based on a 15-ml graduated box sample container from, a Tetra DO test kit, never thought much of the test kit, but I sure liked the sample container.

• By cutting out the wide opposing side, leaving structure at the top,
• wrapping the Tyvek around the container
  • sealed the top where the probe went in with plumbers’ putty.
• The container provided structure and the
• Tyvek was strong enough it protected the reference solution and probe this worked well with my Hanna pH meter and my diy pH probe.

With the Hanna, the response time got into the 20-25 second range, a little bouncing but not bad. I might have been able to do better, certainly I could have worked for a structure that would allow less reference solution, remember maximize surface area, minimize solution.

For many tight areas I have found with good sampling technique you can use the probe as a bench test device.

Let me back up a bit.
The odd thing is CO[SUB]2[/SUB] meters are in my ever-humble-potted-plant- opinion useless when adjusting operational CO[SUB]2[/SUB] levels in aquariums. As with much of the test equipment, they may help understand what worked or tracking over time.

• From an operational point of view, our senses and tuning ourselves to the plants, critters, sights, smells and feel are far more relevant.

I came to my real interest in CO[SUB]2[/SUB] levels from studying circulation issues; I had been sticking test tube drop checkers all over, six to 12 checkers in each of six tanks, placing them based on flow I was tracking principally by dropping different weights of plastic and differing concentrations of Potassium permanganate around the tank.

I wasn’t as smart as Wet to come up with using different values for reference solutions to nail the CO[SUB]2(aq)[/SUB] with some precision.

• Had Wet been around instead of that clown Czado, who knows I may have never purchased a CO[SUB]2[/SUB] meter?

Once it occurred to me that, the alkalinity in our aquariums is about 99% bicarbonate the use of a pH meter made sense, from there it was an easy step to the diy probe, the results were perplexing and on I went to proper CO[SUB]2[/SUB] meters with ion specific probes.

The better the equipment got, the more confused I became, I got mainly catcalls here and demands I get things calibrated, it did not change the results and I notice as more people get the equipment they get the same results, though for some reason no demand everything be calibrated, suddenly, factory calibration and reference solutions are enough.:surprise:

Biollante

 

Pretty Much You & Hoppy Set The Terms

Hi Tom,

Yes, I should have been clear; bicarbonate is about 99% of the alkalinity in my water,

• I suspect that it is for most tap water at least based on the sampling of water reports, granted not comprehensive, of folks in this forum.
• Also granted that in some of those water reports there is not enough information to be conclusive.
  
• Based on my (granted, limited) observations ammonia/ammonium (rotting material? High DOC?) appear to be the bigger interferences.
  
• But I accept your rebuke.

Fully agree with reference samples being important.

The specific reference to surface area to volume was based on

1. speed of stable reading an issue you and Hoppy introduced at the time.
2. An important reason mentioned was mobility,
   1. the reason I cared about, mention and tested for structural integrity.

I never claimed that reducing the amount of reference solution increased accuracy or precision,

• the thing that amazed me was that they were as accurate as they were.
• As I recall the accuracy, comparison was with drop checkers.

I suggested baking soda as opposed to washing soda, due to the availability and that among us poor schmuck hobbyists it is the reference available.

I cannot think of a single original thing I have come up with here, primarily I try things other folks say, many times it is months or even years before I can draw a conclusion and I end up applying to another situation. Early on you derided me for it, I still do not understand why you or anyone should object to repeatability.

My interest in testing the membranes was for usability and reasonable (for a hobbyist) accuracy.

As demonstrated the placing the pH probe into an oversized drop checker gave improved accuracy (compared to drop checkers), but took 30-minutes to an hour to stabilize and had a great deal of lag in reporting change.

As I think, I mentioned these probes are not going to compete with even the cheapest CO[SUB]2[/SUB] probe and meter on the market.

I do not ever recall thinking using paintball cartridges to create a reference solution, though sparging is a recognized method.

I also agree dry ice is wonderful, I use a lot of it.

Calibration certification is expensive and for the hobbyist purposes uncalled for, I am never going to deal with a sample that requires me to be within 2-parts per billion. A reasonable reference standard with the emphasis on repeatability is in my ever humble-potted-plant opinion far more important than precision instrumentation.

Across the board, I tend to think the obsession with numbers in parts per whatever, borders on the ridiculous.

Never really asked anyone not to be skeptical, in fact, I guess what has troubled me most is that when looking for help with methodology or in figuring out which way to go with something, little more than derision. It is okay I have the means to hire whatever help I need.

It doesn’t matter either another person can do it or not. I work hard to keep the language understandable and it will be easier shortly for me to post the methodology and my nifty collection of calibration certificates.

A nice person offered me some materials to work with, I appreciate the confidence in me, but I think the more people trying things and reporting the results the better. But no one should be offended that those of us lacking formal education is these should use precisely the language and parameters you and your acolytes set forth.

I think this stuff is fascinating, I have no fear of changing my view based on evidence, and I do so all the time, part of what I love about this site.

In some areas, I have entirely changed my views from what they were two years ago and honestly, I hope that is the case two years from now.

There is no need for straw dog arguments.

Biollante